1. Field of the Invention
The invention relates to an adjustable iris-diaphragm controller, more particularly to an adjustable iris-diaphragm controller with a control module for controlling a brushless direct current motor to adjust an aperture defined by an iris.
2. Description of the Related Art
FIG. 1 illustrates a known arrangement of a brushless direct current (DC) motor 21, and a Hall sensor (H). The DC motor 21 has a rotor (R), and a stator (S) surrounding the rotor (R). The Hall sensor (H) detects the angular position of the rotor (R) of the DC motor 21, and is disposed adjacent to the rotor (R). First and second transistors (Q1, Q2) are coupled electrically to the Hall sensor (H) and the stator (S).
In operation, when the south pole of the rotor (R) is proximate to the Hall sensor (H), the Hall sensor (H) generates a relatively large output voltage sufficient to activate the first transistor (Q1). The activation of the first transistor (Q1) causes the flow of current (i1) through the stator (S), which results in counterclockwise rotation of the rotor (R). On the other hand, when the north pole of the rotor (R) is proximate to the Hall sensor (H), the Hall sensor (H) generates a relatively large output voltage sufficient to activate the second transistor (Q2). The activation of the second transistor (Q2) causes the flow of current (i2) through the stator (S) to permit further counterclockwise rotation of the rotor (R).
It is known to employ DC motors, such as stepper and servo motors, to adjust an aperture defined by an iris in an adjustable iris-diaphragm controller. However, these types of DC motors are relatively expensive to implement and require complicated control circuitry.
To the applicant's knowledge, conventional adjustable iris-diaphragm controllers do not use a brushless DC motor due to the lack of an appropriate control module that is relatively inexpensive and that is capable of controlling the brushless DC motor to adjust the aperture defined by the iris to a desired setting within a relatively short period of time.